Unknown,Transcriptomics,Genomics,Proteomics

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Whole genome sequencing of Salmonella enterica serovar Typhimurium directed evolution experiment, involved continuous exposure of planktonic cells or biofilms to subinhibitory concentrations of acriflavine or phenylalanine-arginine β-naphthylamide (PABN)

ABSTRACT: We previously developed a directed evolution model that passaged biofilm populations of in S. Typhimurium under antibiotic stress, which identified trade-offs between biofilm formation and antibiotic resistance, conferred by increased efflux activity (Trampari et al., 2021). We applied this same model to expose biofilm populations of S. Typhimurium to RND efflux inhibitor PAβN or non-antibiotic efflux substrate acriflavine. The aim was to identify mutations responsible for restoring biofilm formation in populations exposed to PAβN and to identify how cells in the biofilm can upregulate efflux in the presence of acriflavine. We hypothesised that comparing the mutations selected in both conditions would identify intersecting regulatory relationships between efflux activity and biofilm formation. Parallel linages of S. Typhimurium were grown on glass beads and in planktonic culture in the presence of a subinhibitory concentration of PAβN or acriflavine (or an untreated control) and passaged into new treated media every 48-72 hours. After one, five and ten passages (corresponding to 2, 17 and 35 days of continuous exposure), the populations were stored, DNA was extracted and sequenced to determine mutations selected in these conditions. We compared mutations from conditions treated with efflux substrates to untreated controls in planktonic and biofilm conditions. To explore phenotypic heterogeneity in these populations, we streaked biofilm populations from passages five and ten onto LB agar and picked three single colonies at random to sequence alongside the populations.

INSTRUMENT(S): NA, NextSeq 500, Quick-DNA 96 kit (Zymo)

ORGANISM(S): Salmonella enterica subsp. enterica serovar Typhimurium

SUBMITTER: Emma Holden

PROVIDER: E-MTAB-16846 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Background: Biofilm formation by Salmonella species enhances the capacity of these pathogenic bacteria to survive stresses that are commonly encountered within food processing and during host infection. The persistence of Salmonella within the food chain has become a major health concern, as biofilms can serve as a reservoir to contaminate food products. While the molecular mechanisms required for the survival of bacteria on surfaces are not fully understood, transcriptional studies of other bacteria have demonstrated that biofilm growth triggers the expression of specific sets of genes, compared with planktonic cells. Until now, most transcriptomic studies of Salmonella have focused on the effect of infection-relevant stressors on virulence and on comparing mutant and wild-type (WT). However little is known about the physiological responses taking place inside a Salmonella biofilm. Results: We have determined the transcriptomic and proteomic profiles of biofilms of Salmonella enterica serovar Typhimurium. We discovered that 124 of detectable proteins were differentially expressed in the biofilm compared with planktonic cells, and that 10% (433 genes) of S. Typhimurium genes showed a biofilm-specific pattern of transcription (i.e. a 2-fold or more change in the biofilm compared with planktonic cells). The genes that were significantly up-regulated implicated specific cellular processes in biofilm development including amino acid metabolism, cell motility, global regulation and tolerance to stress. We found that the most highly down-regulated genes in the biofilm were located on Salmonella Pathogenicity Island 2 (SPI2), but that a functional SPI2 secretion system regulator (ssrA) was required for WT biofilm formation. We identified STM0341 as a gene of unknown function that was needed for WT biofilm growth. Genes involved in tryptophan (trp) biosynthesis and transport were up-regulated in the biofilm. Deletion of trpE led to a decrease in bacterial attachment and we show that this biofilm defect is restored by exogenous tryptophan or indole. Conclusion: Biofilm growth of S. Typhimurium causes distinct changes in gene and protein expression. Our results show that aromatic amino acids make an important contribution to biofilm formation, and reveal that SPI2 genes, required for virulence in host cells, show opposing patterns of expression to biofilm-specific genes in S. Typhimurium. Overnight cultures of SL1344 grown in CFA broth were standardized to achieve an initial concentration of 10^6 CFU ml-1 and injected into a stirring influent flask containing 5 L of pre-warmed (25C) sterile CFA medium. The inoculated influent was then pumped through silicon tubing (5 mm internal diameter, Samco Silicon Products Ltd.) at 60 ml h-1 using a peristaltic pump (Minipulse 3, Gilson). The bacteria were allowed to flow through the closed system and either attach to a vertical piece of silicon tubing (1 meter length, 16 mm internal diameter, Samco Silicon Products Ltd.) or flow out into a waste reservoir. The tubing was positioned vertically to collect biofilm cells adherent to the tubing and minimise collecting bacteria that had simply sedimented. Possible backflow of media or bacteria into the influent from the silicon tubing was eliminated using media breaks. Samples taken to determine the pH of the medium or bacterial cell counts were removed via a media port located near the effluent and influent vessel, respectively. Planktonic cells were removed after 72 h of growth from the influent vessel to avoid any contamination with biofilm cells. The entire system was kept at a constant temperature of 25C and biofilm cells were isolated after 72 h of growth. All planktonic and biofilm samples were isolated from the same experimental system and used for both RNA and protein isolation. For this study, four biological replicates were performed at four different dates (Jun25, Jul5, Jul16, Oct11; as indicated in the sample title). For the dual-colour microarray hybridisations, we used Salmonella genomic DNA as the comparator which also acted as the control for spot quality. Individual labelled cDNA samples (RNA) were hybridised up to 4 times (technical replicates).

Project description:Acinetobacter baumannii has emerged as one of the most problematic opportunist bacterial pathogen responsible for hospital-acquired and community infections worldwide. Besides its high capacities to acquire antibiotic resistance mechanisms, it also presents high adhesion abilities on inert and living surfaces leading to biofilm development, a lifestyle conferring an additional protection against various treatments, and allowing it to persist for long periods in various hospital niches. Due to their increasing resilience to antimicrobial treatments, A. baumannii biofilms are difficult to control and ultimately eradicate. Overcoming the significant challenges pose by A. baumannii require fundamental insights into mechanisms involved in the development of mature biofilm and thus, may help to develop novel strategies for biofilm prevention and control. To unravel critical determinants of this sessile lifestyle, we compared the proteome profiles of bacteria grown in planktonic stationary phase with those of two A. baumannii strains (ATCC 17978 and SDF), harboring specific features regarding biofilm formation, grown in mature solid-liquid (S-L) biofilm using a proteomic quantitative study. Of interest, among the 69 common proteins determinants accumulated in the two strains at the S-L interface, we sorted out the MacAB-TolC system. This tripartite efflux pump appears to play a role in A. baumannii biofilm formation as demonstrated by using ΔmacAB-tolC deletion mutant. Complementary approaches allowed us to get an overview of the impact of macAB-tolC deletion in A. baumannii physiology. Indeed, this efflux pump appeared to be involved in the envelope stress response occurring in mature biofilm and contributes to maintain WT membrane rigidity as well as tolerance to high osmolarity conditions. In addition, this system is probably involved in the maintenance of iron and sulfur homeostasis. MacAB-TolC might help this pathogen facing and adapting to biofilm architecture which is heterogeneous in space and time, especially in mature biofilm. Increasing our knowledge of A. baumannii biofilm formation will undoubtedly help us develop new therapeutic strategies to tackle this emerging threat to human health.

Dataset Information

Whole genome sequencing of Salmonella enterica serovar Typhimurium directed evolution experiment, involved continuous exposure of planktonic cells or biofilms to subinhibitory concentrations of acriflavine or phenylalanine-arginine β-naphthylamide (PABN)

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